Hertzian stress-reducing means for gears

ABSTRACT

Reduction in Hertzian and bending stresses in gears and in bearing assemblies is achieved by new configurations of gears and bearing assemblies employing combinations of materials in selected areas of the gears or bearing assemblies or cutting narrow slots into selected areas of the gear teeth or bearing assemblies. The increase in life of the gear or bearing assembly is expressed as L1 cH/H1n. For gears n 6.5 for bearings n 9. The Hertzian stress reduction provides in addition to increased operating life, higher reliability, higher load-carrying capacity and gears or bearings of quieter running characteristics at higher rotational rates than gears and bearings in the prior art.

0 United States Patent [151 3,636,792

Vigh 51 Jan. 25, 1972 [54} HERTZIAN STRESS-REDUCING MEANS 3,173,3013/1965 Miller ..74/46l X F EARS 3,304,795 2/1967 Rouveral ..74/4l 1 on G3,504,562 4/1970 Hirych ..74/46l X [72] Inventor: Zohnn Vigh, 112 NorthMar Vista Ave,

Pasadena, Calif. 91906 Primary ExaminerLeonard H. Gerin Filcd: Sept.1969 AnorneyNorman L. Chalfin [21 App]. N6; 862,612 [51] ABSTRACTReduction in Hertzian and bending stresses in gears and in [52] U.S. Cl..74/46l, 74/411 bearing assemblies is achieved by new configurations ofgears {51] ..Fl6h 55/14, F16h 57/00 and bearing assemblies employingcombinations of materials [58] Field of Search ..74/461, 411, 243 PC,440, 446, in selected areas of the gears or bearing assemblies orcutting 74/441 narrow slots into selected areas of the gear teeth orbearing assemblies. The increase in life of the gear or bearing assemblyis [56] Referen e Cited expressed as L,=cH/l-l,n. For gears n=6.5 forbearings n=9.

The l-lertzian stress reduction provides in addition to in- UNITEDSTATES PATENTS creased operating life, higher reliability, higherload-carrying capacity and gears or bearings of quieter runningcharacxjigi teristics at higher rotational rates than gears and bearingsin 1,772,986 8/1930 Dunham ..74/461 the 2,335,504 1 1/1943 Gazda....74/46l X 9 Chin, 21 Drawing Figures 2,530,767 11/1950 l l am1l l..74/46 1 X sissegvez PATENTED JANZS I972 SHEET 1 OF 6 FIG.6

INVEN TOR.

Z0 LTAN VIGH HERTZIAN STRESS-REDUCING MEANS FOR GEARS BACKGROUND OF THEINVENTION In my US. Pat. No. 3,337,278 issued Aug. 22, 1967 entitledHIGH SPEED ROLLER BEARING I disclosed and claimed roller bearingelements and ball bearing elements of reduced weight including internalareas filled with relatively yieldable or compressible materials, orwith bearings alternatively being hollow. Where roller bearing elementswere disclosed they included end seals in the form of discs to prevententrance of lubricants into the hollow areas of the interior or into thefilled areas. It was shown in the above-identified patent how thereduction of mass and increased yieldability of the bearing surfacesincreased their lifetime greatly.

THE PRESENT INVENTION The present invention contemplates improvementupon the bearing devices of the earlier invention and is also applicableto gears as well. According to the present invention means are providedby which the failure of gears and bearing assemblies due to high contactand bending stresses can be substantially reduced and their lifeextended many fold where the stresses occur cyclically.

Contact stresses are called Hertzian stresses. Such stresses areexperienced at the tooth-contacting surfaces in meshed or loaded gears.The material of the solid tooth under load at the contact area sufferslocal high-elastic compression and shear stresses. The residual plasticdeformation might be higher than the limit of the material of which thegear is made. The same considerations apply to bearing assemblies.

According to this invention the gear teeth are modified so as to includemeans which provide a yieldability such that contact depth and Hertzianstress at the contact areas are reduced. As modified the gear teethcomprise what amounts to a coating and a yieldable core. The core then,suffers compression and shear stresses and the coating suffers mainlybending stress, and some compressional stress under load.

The modulus of elasticity of the core material is such as to be lessthan the modulus of the surface material. In one mode of making thecombinational material gear of this invention well-known coating systemscan be used such as diffusion of coating material, hard facing, or flamehardening, etc. Metallurgical compatibility between core and coatingmaterials is necessary. Chromium, phosphates, nitrides and oxides, etc.,can provide the hard surface materials on the gear since they have goodthermal conductivity, can reduce friction, wear, oxidation heating andprovide good corrosion resistance. The coatings should form a thicknessof to percent of the gear tooth thickness at the pitch line.

As another mode of Hertzian stress reduction a slot can be cut into thegear tooth. The slot configuration can be selected from a number ofalternatives to reduce concentrations of stress in the root radius area.Slotting can be achieved by highenergy and high-density laser beam orelectron beam-cutting techniques to provide slot widths of from 0.00025to 0.001 inch. The slot can be filled with an elastomeric material toreduce any likelihood of contamination.

The outer and inner ring structures of ball bearing assemblies can bemade according to the invention by enclosing the bearing race with ayieldable material, or by making the materials of the rings and raceundercut over a portion of their adjoining surfaces so that the opposedundercut areas, so to speak, breathe as the roller or ball roll withinthe assembly.

Slots can also be cut into the bearing assembly rings in such a mannerthat the stresses are relived and the life of the assemblies extendedimmeasurably.

As a further example of the combinational materials technique of thisinvention for Hertzian stress reduction coatings of resilient materialsare provided on the inner and outer ball bearing race structures.

In yet another example of the stress relief techniques ball bearingassemblies have either outer or inner circumference crenelations whichprovide alternate contacting and noncontacting areas where the ballbearing race is inserted in its receptacle or positioned on its shaft.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 illustrates a materialcombination gear tooth configuration according to this invention where acore and a coating are involved;

FIG. 2 is an illustration of a slotted tooth according to the inventionwherein the slot is cut vertically down the center of the tooth;

FIG. 3 is an illustration of an inverted V-shaped slotted gear tooth;

FIG. 4 is an illustration of a gear tooth according to the inventionwherein the slot is in the shape of an inverted Y";

FIG. 5 is a variant of the gear of FIG. 4 with a slot in the form of aninverted Y";

FIG. 6 is an illustration of an alternative form of the inverted V slotin a gear tooth wherein the slot follows the contour of the gear tooth;

FIG. 7 is an explanatory diagram showing the contact ellipse area on agear tooth;

FIG. 8 is a graph of showing the solution for the dimensionless value ofthe life factor L utilizing values of Hertzian stress and elasticdeformation of the surface of a gear tooth;

FIG. 9 is a graphic chart showing the comparative reliability of priorart gears and gears with teeth treated in accordance with thisinvention;

FIG. 10 is a section through a ball bearing inner and outer ringstructure utilizing Hertzian stress reduction configurations accordingto this invention;

FIG. 11 is a section through a ball bearing assembly similar to that inFIG. 10 wherein another mode of assembly of the components thereof isshown;

FIG. 12 is a section through a bearing assembly similar to that of FIG.10 and 11 illustrating another form of application of the invention;

FIG. 13 is an illustration of the use of relief space as a Hertzianstress reduction means in a ball bearing assembly;

FIG. 14 is an illustration showing a cross section through a ballbearing assembly where a slotting technique is used for Hertzian stressreduction;

FIG. 14a is a side view of FIG. 14.

FIG. 15 illustrates the use of a resilient coating on the outer surfacesof a ball bearing assembly for Hertzian stress relief;

FIG. 16 illustrates an alternative means for the placement of yieldablematerial such as a resilient coating on the inner surfaces of a ballbearing receptacle;

FIG. 17 is an illustration of the use of undercut relief areas in theshaft and housing of a ball bearing receptacle;

FIG. 18 is a composite drawing showing in one-half the use of an innercircumference crenelation on a ball bearing assembly, and in the otherhalf an outer circumference crenelation for Hertz stress reductionaccording to the invention;

FIG. 19 is an illustration of the application of Hertz stress reductionto a roller; and

FIG. 20 is a graph to show the improvement in life expectancy throughthe use of Hertzian stress reduction techniques of this invention.

DESCRIPTION OF THE EMBODIMENTS As has been described hereinabove thepresent invention contemplates the reduction of Hertzian Stress andcontact and bending stress on the surface of gear teeth and bearingassemblies by modification of the structures of such gear teeth and ballor roller bearing assemblies. The reduction is accomplished in twoalternative modes. One of the modes is as illustrated in FIG. 1 forgears employing a combination of materials. This mode is alsoillustrated in FIGS. 10, 11 and 12, and others for ball bearingassemblies. A second mode is to slot the structure of the gear tooth asin FIGS. 2-6. Slotted bearing assembly technique is illustrated in FIG.14.

Referring now particularly to FIG. 1, a typical gear tooth is shown witha portion of the point cut away to show how a tooth according to theinvention is constructed utilizing combinational materials. The toothcomprises a core 11 over which there is a coating 12 of uniformthickness. The core 11 may be fabricated out of a material which has amodulus of elasticity less than that of the coating material 12. Thecoating material may be applied by any known technique such asdiffusion, hard facing, flame hardening, etc. The material of thecoating 12 may be any material compatible with the core 11 from ametallurgical standpoint. The coating may be such materials as chromium,phosphates, nitrides or oxides, etc., that produce a high-thermalconductivity, have good anticorrosion properties, and can reducefriction, wear, heating and oxidation. The thickness of the coating hasbeen found to be best at from to percent of the thickness of the geartooth 10. The core 11 may be of a metal such as aluminum or anonmetallic material.

In FIG. 1 a dashed outline 13 is shown of a tooth in mesh with a toothcoated according to the invention 10). Were the elastic shell formed bycoating 12 not present there would be no deformation, producing a stressat the root junction 14. But since the coating 12 bends, as indicated bydashed lines 15, into the core 11, which is yieldable relative to thecoating 12, the stress at 14 does not occur, thereby increasing the lifeof the tooth, making it operable over many more cycles and at anincrease in cyclic rate which would destroy conventional gear teeth in arelatively short time. The contact depth under load at the pitchdiameter point (15) with the combinational material tooth of thisinvention is less than with a solid tooth giving rise to longer wear.

One of the factors which is responsible for wear in a solid tooth is theultimate breakdown of lubrication due to compression against anonyielding surface. When the elastic surface provided by thecombinational materials 11,12 of this invention are employed theyielding surface provides a rolling path over which the lubricant canflow without being destroyed by the compressional forces.

In FIGS. 2-6 inclusive are shown a number of slotting configurationswhich can be applied to gear teeth for Hertzian stress reductionaccording to this invention. The slots are cut to a thickness of from0.00025 to 0.001 inch To out such fine slots modern laser and electronbeam-cutting techniques are employed.

In FIG. 2 a gear tooth 20 is shown with a vertical slot cut through thetooth between opposite faces of the gear. The slot 21 begins at point 22of the gear tooth and extends downward to a predetermined depth 23 whichmay beat any point above or below the root diameter 24 of the gear 25.Thus the driving tooth 26 shown in dashed lines upon contacting tooth 20will have its compressional force distributed throughout the gear asindicated by circular dashed lines 27.

A pair of slots 31,32 are shown in FIG. 3 cut into a gear tooth 30 inthe form of an inverted V." The slots generally follow the contours ofthe flank and face 34 of gear tooth 30 starting from two adjacentpositions 35,36 on the point 33 of tooth 30. The angle between the Vcomponents may be varied to suit different load conditions.

An inverted Y shaped slot 41 is cut into tooth 40 as shown in FIG. 4.The diverging slots 42,43 of the Y" may be varied in angle and theirstarting point on the tooth may be above or below the pitch diameterline 44 of tooth 40 to accommodate different loading conditions. Thevertical slot of Y" 41 extends to point 46.

An alternative form of inverted Y" slot 51 is shown in FIG. 5 where thediverging slots 52,53 in slot 51 tend to follow the tooth face contourto a greater degree.

An alternative inverted V" configuration for slot 61 in tooth 60 isshown in FIG. 6. Slot 61 is cut so as to be entirely within the contourof gear tooth 60 having no edge exit on any part of the tooth. Theconfiguration of slot 61 islike that of a bent hairpin within tooth 60.The stiffness of tooth 60 is determined by the diverging angle of slotends 63,64 from bend 62.

The slotting configurations shown in FIGS. 2 through 6 are applicable toany type of gears, for example, spur, helical, bevel, spiral, hypoid,etc. The slots shown in the figures can have a variety of shapes bywhich Hertzian stress is reduced at the area of contact which is usuallydescribed as on the pitch circle. The area of contact is also usuallydescribed as having an ellipsoidal shape on the face of the gear tooth.The slots 21, 31, 32, 41, 51, and 61 can reduce the concentration ofbending stress in the root radius area and results in a favorable loaddistribution at the critical sections of the gear. The slots may befilled with elastic material to protect them from contamination.

It has been previously mentioned that high energy and highdensity laserbeams or electron beam cutting may be used to cut the slots hereinabovedescribed. In the cutting operation the high-kinetic energy istransformed into heat which on impact with the tooth causes rapid highlylocalized melting. This does not deform the gear because of the rapidityof action and its localized nature.

With either the combinational material form of gear tooth shown in FIG.1, or with the slotted tooth gear configuration shown in FIGS. 2-6, theyieldability of the gear faces that results tends to equalize minorinaccuracies of tooth geometry and the overlapping of tooth motion istransmitted smoothly and quietly compared with gears not so treated ashereinabove described. The gears need not be so closely machined as isrequired for high-precision quiet running gears and accordingly will beless costly for operation with the equivalent results. The gearsaccording to the above-described configurations absorb shock andvibration and compensate for machining error and mounting inaccuracies.The slotted gears of this invention provide corrective action across thefull face width of the gear mesh equalizing the contact depth throughoutthe tooth surface so that perfect gear operation with high reliabilityand longer life can be assured.

As has been mentioned above in connection with the diverging slots 63,64of Y" slot 61 in FIG. 6, the diverging angle ofthe V" slots 35,36 inFIG. 3, and 42,43 in FIG. 4 and the slots 52,53 may vary in angle fordiffering degrees of load and stiffness. The vertical slot 21 and 31,32,42,43, and 52,53, 63,64 will produce greater or lesser tooth stiffnessdepending upon the depth to which they are cut into their respectiveteeth, 10, 20, 30, 40,50, 60.

The reduction of Hertzian stresses by the design and configurationshereinabove described improves boundary lubrication because an elastichydrodynamic film can develop to separate meshing surfaces. At thecontact ellipse (see FIG. 7) the contact depth becomes smaller reducingshear stress. At the same time tooth wear is reduced because the load isgradually transferred from tooth to tooth with less sliding frictionbetween teeth during engagement. This provides greater efficiency,longer life for a given load, and less noise in operation.

The gears which have been described hereinabove are configured to beyieldable when engaged by teeth of another gear. In one form the toothof the gear is made of a combination of materials comprising a corehaving one modulus of elasticity and a coating on the core having ahigher modulus of elasticity. The tooth is thus yieldable under Hertzianstress to reduce wear and noise and to increase gear life. In anotherform slots of thin cross section are cut into the tooth in variousconfigurations making the surface yieldable under Hertzian or cyclicstress conditions.

In FIG. 7 the face 71 of a typical gear tooth is shown. On face 71 isdrawn the representation 72 of a contact ellipse at a point on the faceof the tooth where Hertzian or compressional stress has occurred,depressing the surface to a maximum depth shown at 73. The points 74 ofthe contact ellipse are the points of maximum shear stress.

In FIG. 8 a graph is shown of the solution of the formula for thedimensionless life factor L,.

L is the gear life in revolutions x 10 c is a constant H is a calculatedI-Iertzian stress for a gear H is the l-Iertzian stress reduction due tothe combinational material or slotting technique of this inventionapplied to the gear.

The Hertzian stress values are expressed in p.s.i.

In the graph I-lertzian stress values in p.s.i. are listed on the leftordinate 80. The elastic deformation (contact depth as illustrated inFIG. 7) is the scale on the right ordinate 81 in microinches. A line 82plotted on the graph of FIG. 8 shows the empirical test curve for gearsgiving the actual life vs. contact stress derived by this inventor fromdata appearing in current gear literature. Gear life is represented inline 82 in revolutions.

The lower abscissa 83 of the graph in FIG. 8 is the load on a singletooth of a gear represented in lbs. The upper abscissa 84 of the graphis gear life in revolutions x The curve 85 on the graph is the result ofa single calculation for one gear made under varying load conditions.The curve 86 is the result of a calculation for the same gear for whichthe curve 85 was drawn to show the elastic deformation of the contactarea under load as was shown in FIG. 7.

For a gear with one tooth on which is impressed a load of 500 lbs. (seepoint 87 on curve 85 of the graph of FIG. 8) the gear life will be 6X10revolutions, as seen at point 88 on the upper abscissa line 84, and anelastic deformation of 500 microinches (due to I-Iertzian stress) asindicated at 89 on curve 86 of FIG. 8. When the gear is treated with thecombinational materials technique (FIG. 1) or any of the slotted toothtechniques (FIGS. 2-6) the elastic deformation is reduced to 320microinches, as can be seen at 92 on curve 86 of FIG. 8. At adeformation depth of 500 microinches the l-lertzian stress is 262,000p.s.i. which is indicated at 87 on curve 85 of FIG. 8 while at anelastic deformation of only 320 microinches the Hertzian stress value isonly 202,000 p.s.i. as indicated at 90 on curve 85.

From the formula for L previously stated using the value of l for theconstant c, L =5.42 (91, FIG. 8). The increased life of the gearaccording to this invention is therefore 6X10, (L)X5.42, (L,)=32.52 1Orevolutions.

In FIG. 9 a chart is drawn showing the reliability of prior art gearscompared with gears treated in accordance with the Hertzian stressreduction techniques of this invention. The left ordinate 94 lists thepercent reliability of gears. The right ordinate shows the failurepercentage of gears. The values on opposite ends of any horizontal linebetween the ordinates 94 and 95 can be seen to add to 100 percent. Thelower abscissa 96 represents the number of revolutions of a gear atwhich failure can be expected. The curve 97 drawn on graph of FIG. 9 isa failure curve derived from a large number of tests of prior art gears.The curves 98 and 99 define the range within which the life expectancyof similar gears treated according to this invention for Hertzian stressreduction.

Hertzian stress reduction configurations are also feasible according tothis invention for ball bearing assemblies. One such arrangement isshown in FIG. 10.

A ball bearing inner and outer ring structure are shown in FIG. 10 insection, wherein a solid ball 100 is installed in an inner ball bearingrace 101 fabricated of a hard material, such as hearing steel.Surrounding the race 101 is a yieldable encasement 102 which may be of ametallic or nonmetallic material.

In FIG. 11 an inner and outer ring configuration similar to that shownin FIG. 10 is illustrated in section wherein the inner ring 105 has atwo piece outer ring 106,107 pressfitted thereover. Outer rings 106,107are of a yieldable material similar to that of encasement 102, in FIG.10.

A bearing configuration similar to that in FIGS. 10 and 11 is shown inFIG. 12 wherein a hard coating race surface 110 is applied to the outerand inner ring surfaces 111.

In FIG. 13 the ball 100 is surrounded by a pair of concentric rings121,122 of identical material. However, there is an undercut reliefspace 123 between the two rings 121, 122 so that under load the rings121 and 122 are yieldable.

It can be seen here that the bearing configurations shown in FIGS. 10-13are so arranged that there is a yielding material somewhere to reducethe I-Iertzian stress. In FIGS. 10, 11 and 12 the yieldable materials102, 111, 106, and 107 are different from (that is, softer than) thebearing race materials 101, and 105. However, the materials of both raceand ring in FIG. 13 are the same. Nevertheless in all the configurationsyieldability is present under load.

The configurations of FIGS. 10 to 13 inclusive fall within the samecombinational materials techniques described in connection with FIG. 1for gears, where a yieldable core material has a surface coating with alower modulus of elasticity that is in contact with the loading ordriving surface.

FIG. 14 illustrates a slotting technique for Hertzian stress reductionby which a yieldable loading surface is achieved for ball or rollerbearings. The inner and outer rings in FIG. 14 as seen at 125 and 126are slotted as at 127 and 128. Slot 127 is cut into the ring from theleft side. Slot 128 is cut from the right side. Neither slot goescompletely through the ring into which it is cut. Not shown herein but afurther extension of the technique illustrated in FIG. 14 is to cutalternate slots from either side into each ring such as 125 and 126. Thedegree of yieldability would be a function of the number of alternateslots cut into each ring.

FIG. 15 illustrates the manner in which a resilient coating such as, forexample, synthetic rubber as at 130 is deposited on the outer surfacesof the inner and outer rings 131,132 of the ball bearing race.

In FIG. 16 an alternative to the yieldable material placement of FIG. 15is shown wherein the resilient (yieldable) coating 141 is applied to theinner surfaces of a ball bearing race receptacle bore 142.

In FIG. 17 a ball bearing receptacle bore is shown where the shaft 151is undercut as at 152 and the housing 153 is undercut as at 154 so as topermit the yielding of rings of the bearing assembly under load wheninstalled in receptacle 150.

In FIG. 18 a composite drawing of half of each of two ball bearingassemblies is presented to show that either of the outer or inner (161)circumferences of the assembly may be crenelated. Ball bearing assembly163 fits over a shaft, or housing to permit inner surface 161 to yieldunder load. Assembly 162 fits within a housing or shaft permitting theouter crenelated surface 160 to yield under load.

In FIG. 19 there is shown another form of combinational materialapplication of the Hertzian stress reduction technique of thisinvention, applied to a roller 180, on which bearings according to thisinvention can be installed. Within roller 180 end caps 18] are insertedsealably, at opposite ends. The caps 181 are of porous material so thatsubstances such as a lubricant 183 may be disposed within the hollowarea 182 of roller 180 and very slowly seep out through the pores of thecaps 181 to lubricate the bearing races or assemblies installed on therollers 180. By this means long storage of bearings can be achievedwithout need for constant relubrication thereof.

In FIG. 20 a graph is shown of the improvement in life expectancy forbearings using the techniques of Hertzian stress reduction hereinabovedescribed for antifriction bearings. The ordinate in the graph of FIG.20 gives bearing life in millions of revolutions. The abscissa 171 isthe percent of bearings failed. The curve 172 gives the life expectancyfor conventional bearings of the prior art, as determined from a greatmany tests. The curve 173 shows the expected life of bearings afterHertzian stress treatment as disclosed hereinabove. For bearings thelife expectancy formula is L =c (H/H,) It will be noted that this is thesame formula as previously set forth for gears to which l-lertzianstress reduction has been applied according to this invention, exceptthat for bearings the exponent is larger. Accordingly the graph of FIG.8 may be applied to ball and roller bearing structures so treated,except that the slopes of the curves will differ, being shallower.

Similarly the curves in the graph of FIG. 9 may be applied to bearingsexcept that the slopes will be different.

What is claimed as new is:

1. In mechanical assemblies such as gears and bearings, means forreducing the Hertzian stresses thereon comprising: slots cut into saidassemblies having cross sections on the order of 0.00025 inch to 0.001inch in predetermined configurations, said slots being filled with anelastomeric material to protect them from contamination.

2. The slots defined in claim 1 being cut into said assemblies fromopposite sides thereof.

3. The slots defined in claim 1 being cut into said assemblies in theform of an inverted V.

4. The slots defined in claim 1 being cut into said assemblies in theform of an inverted Y.

5. The slots defined in claim 1 being cut into said assembliesvertically.

6. In a gear, a gear tooth having slots cut into said tooth, said slotshaving a cross section of between 0.00025 and 0.00l inch and beingfilled with an elastomeric material to prevent contamination of saidslot, whereby said gear tooth operates with reduced Hertzian stress andhas increased wear and life expectancy.

7. In the gear tooth defined in claim 6 the configuration of said slotbeing in the form of an inverted V.

8. In the gear tooth defined in claim 6 the configuration of said slotbeing in the form of an inverted Y."

9. The gear tooth defined in claim 7 including a slot vertically cutinto the tooth.

UNITED STATES PATENT OFFICE CERTIFICATE OF QQREC'HO January 25, 97

Patent No. 3,636,792 Dated lnventofls) Zoltan Vigh It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the cover sheet [721 in the inventor's address, the zip code "91906"should read 91106 In the Abstract the formula should read:

L c (ii/H n Signed and sealed this 12th day of December 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents ORM (10-69) uscoMM-oc scan-ps9 fi U.S. GOVERNMENT PRINT'NGOFFICE 2 I959 36G-33L

1. In mechanical assemblies such as gears and bearings, means forreducing the Hertzian stresses thereon comprising: slots cut into saidassemblies having cross sections on the order of 0.00025 inch to 0.001inch in predetermined configurations, said slots being filled with anelastomeric material to protect them from contamination.
 2. The slotsdefined in claim 1 being cut into said assemblies from opposite sidesthereof.
 3. The slots defined in claim 1 being cut into said assembliesin the form of an inverted ''''V.''''
 4. The slots defined in claim 1being cut into said assemblies in the form of an inverted ''''Y.'''' 5.The slots defined in claim 1 being cut into said assemblies vertically.6. In a gear, a gear tooth having slots cut into said tooth, said slotshaving a cross section of between 0.00025 and 0.001 inch and beingfilled with an elastomeric material to prevent contamination of saidslot, whereby said gear tooth operates with reduced Hertzian stress andhas increased wear and life expectancy.
 7. In the gear tooth defined inclaim 6 the configuration of said slot being in the form of an inverted''''V.''''
 8. In the gear tooth defined in claim 6 the configuration ofsaid slot beiNg in the form of an inverted ''''Y.''''
 9. The gear toothdefined in claim 7 including a slot vertically cut into the tooth.